In general, an impeller is a rotating body for applying energy to a fluid in a pump, a ventilator, a compressor, etc. When the fluid passes between blades of the impeller rotated at a high speed, energy is supplied from the blades to the fluid, for increasing a pressure and speed of the fluid in an outlet.
A conventional high speed type impeller will now be explained with reference to the accompanying drawings.
FIG. 1 is a perspective view illustrating the conventional high speed type impeller, FIG. 2 is a perspective view illustrating the bottom surface of FIG. 1, and FIG. 3 is a structure view illustrating stress distribution in the high speed rotation of FIG. 1.
As illustrated in FIGS. 1 and 2, the conventional high speed type impeller includes a body 10 having a shaft coupling hole 11 at its center portion so that a rotation shaft (not shown) of a motor can be coupled into the shaft coupling hole 11, and being extended in the insertion direction of the rotation shaft to be bent along a plane surface perpendicular to the rotation shaft direction, and a plurality of blades 20 installed at the bent portion of the body 10 to be bent at a predetermined angle to the rotation shaft direction.
On the bottom surface of the impeller, a motor mounting guide 15 is downwardly protruded from a disk portion 10′ of the body 10 to surround the circumference of the shaft coupling hole 11. The motor mounting guide 15 surrounds the motor inserted into the shaft coupling hole 11, thereby stably coupling the motor into the shaft coupling hole 11.
Normally, the conventional high speed type impeller is rotated at a speed of about 100,000 rpm. Such a speed exceeds a sound velocity. That is, very large centrifugal force is applied to the impeller. Therefore, the impeller needs sufficient durability to endure the centrifugal force.
However, as shown in FIG. 3, in the conventional high speed type impeller, stress concentration occurs at the center portion C of the body 10. As a result, cracks are generated at the center portion C, to damage the impeller.
Actually, when an impeller made of polyphenylene sulfide (PPS) was tested at 80,000 rpm, the maximum stress was about 146 MPa approximate to yield stress (150 MPa) of the PPS.
In this case, even if the rotation speed of the impeller slightly increases, the impeller may be damaged.
In order to prevent the impeller from being damaged by the cracks in the high speed rotation, functional plastic having a high formation temperature such as PEK is applied to the impeller to improve durability. However, since the functional plastic contains a high cost material, the manufacturing cost of the impeller increases.
There are thus increasing demands for a high speed type impeller which can cut down the unit cost of production and ensure durability, by using a low cost material and adding a supplementary device.